Patent GB-389822-A (GB)
Title: Improvements in or relating to electrically-conducting coatings
IPC: H01B1/00
Filed: 1931-09-21
Abstract: A coating-composition contains a finely divided metal powder in suspension in an adhesive liquid which has no appreciable action on the metal powder, and which contains a resin compound and a free acid other than natural resin acid in sufficient quantity to ensure the formation of a coating having an electrical conductivity high enough to be comparable with a metal surface. The composition may be prepared by adding metal powder to a solution of an acidic ester gum (prepared by esterifying rosin or gum dammar with glycerol), in an organic solvent preferably with the addition of a stiffening agent such as a high viscosity cellulose nitrate.  The ester gum may be rendered acidic during preparation by incompletely esterifying the rosin, or by the addition of an acid to the solution.  The preferred acid is acetic acid, but any acid, inorganic or organic may be used. In place of the natural gum a synthetic condensation product containing free acid hydroxyl groups may be employed.  If desired, dewaxed gum dammar may be added to the ester gum solution to increase the adhesiveness.  The preferred solvent is an alkyl ester, e.g. amyl acetate, and the preferred resin is the glycerol ester of gum dammar. In an example three parts of collodion cotton is dissolved in a mixture of amyl acetate, ethyl acetate, butyl alcohol and benzene, added to a quarter of its bulk of a solution containing 5 lb. of ester gum, 4 lb. dewaxed dammar in a similar mixed solvent, and one-eighth of the total bulk of glacial acetic acid is added together with 150-300 lb. of copper powder.ALSO:A metal coating-composition contains a finely divided metal powder in suspension in an adhesive liquid which has no appreciable action on the metal powder and which contains a resin compound and a free acid other than natural resin acid in sufficient quantity to ensure the formation of a coating having an electrical conductivity high enough to be comparable with a metallic surface.  The composition may be prepared by adding metal powder to a solution of an acidic ester gum, (prepared by esterifying rosin or gum dammar with glycerol), in organic solvents, preferably with the addition of a stiffening agent such as a high viscosity cellulose nitrate.  The ester gum may be rendered acidic in preparation by incompletely esterifying the p  resin, or by the addition of an acid to the solution.  The preferred acid is acetic acid, but any acid, inorganic or organic, may be used.  In place of the natural gum, a synthetic condensation product containing free acid hydroxyl groups may be employed.  If desired dewaxed gum dammar may be added to the ester gum solution to increase the adhesiveness. The preferred solvent is an alkyl ester, e.g. amyl acetate, and the preferred resin ester is the glycerol ester of gum dammar.  In an example 3 parts of collodion cotton is dissolved in a mixture of amyl acetate, ethyl acetate, butyl alcohol, and benzene, added to 1/4 of its bulk of a solution containing 5 lbs. of ester gum, and 4 lbs. dewaxed dammar in a similar mixed solvent 1/8 of the total bulk of glacial acetic acid is added together with 150-300 lbs. of copper powder.  The material is suitable for coating the interior of wireless cabinets by spraying such as by a Schoop gun or as an outer coating to valves, or as a coating for paper for use in condensers, and similar applications.